34 files changed, 1232 insertions, 97 deletions

diff --git a/runtime/doc/cmdline.txt b/runtime/doc/cmdline.txt
index 318c699925..8abb16b8c4 100644
--- a/runtime/doc/cmdline.txt
+++ b/runtime/doc/cmdline.txt
@@ -805,6 +805,7 @@ Note: these are typed literally, they are not special keys!
 
 							 *filename-modifiers*
 	 *:_%:* *::8* *::p* *::.* *::~* *::h* *::t* *::r* *::e* *::s* *::gs*
+	        *%:8* *%:p* *%:.* *%:~* *%:h* *%:t* *%:r* *%:e* *%:s* *%:gs*
 The file name modifiers can be used after "%", "#", "#n", "<cfile>", "<sfile>",
 "<afile>" or "<abuf>".  They are also used with the |fnamemodify()| function.
 These are not available when Vim has been compiled without the |+modify_fname|
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 5b5e8fa00d..2a2d601551 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -6053,6 +6053,7 @@ os2			OS/2 version of Vim.
 osfiletype		Compiled with support for osfiletypes |+osfiletype|
 path_extra		Compiled with up/downwards search in 'path' and 'tags'
 perl			Compiled with Perl interface.
+persistent_undo		Compiled with support for persistent undo history.
 postscript		Compiled with PostScript file printing.
 printer			Compiled with |:hardcopy| support.
 profile			Compiled with |:profile| support.
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 0bdde3a556..9c9d584155 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -7220,6 +7220,33 @@ A jump table for the options with a short description can be found at |Q_op|.
 			global
 	Alias for 'term', see above.
 
+						*'undodir'* *'udir'*
+'undodir' 'udir'	string	(default ".")
+			global
+			{not in Vi}
+			{only when compiled with the +persistent_undo feature}
+	List of directory names for undo files, separated with commas.
+	See |'backupdir'| for the format.  Specifically, "." means using the
+	directory of the file.
+	When writing: The first directory that exists is used. "." always
+	works, no directories after "." will be used for writing.
+	When reading all entries are tried to find an undo file.  The first
+	undo file that exists is used.  When it cannot be read an error is
+	given, no further entry is used.
+	See |undo-persistence|.
+
+						*'undofile'* *'udf'*
+'undofile' 'udf'	boolean	(default off)
+			local to buffer
+			{not in Vi}
+			{only when compiled with the +persistent_undo feature}
+	When on, Vim automatically saves undo history to an undo file when
+	writing a buffer to a file, and restores undo history from the same
+	file on buffer read.
+	The name of the undo file is specified by 'undodir'.
+	See |undo-persistence|.
+	WARNING: this is a very new feature.  Use at your own risc!
+
 						*'undolevels'* *'ul'*
 'undolevels' 'ul'	number	(default 100, 1000 for Unix, VMS,
 						Win32 and OS/2)
diff --git a/runtime/doc/tags b/runtime/doc/tags
index 259933eaae..9e2dac5655 100644
--- a/runtime/doc/tags
+++ b/runtime/doc/tags
@@ -10,6 +10,16 @@ $VIM	starting.txt	/*$VIM*
 $VIM-use	version5.txt	/*$VIM-use*
 $VIMRUNTIME	starting.txt	/*$VIMRUNTIME*
 %	motion.txt	/*%*
+%:.	cmdline.txt	/*%:.*
+%:8	cmdline.txt	/*%:8*
+%:e	cmdline.txt	/*%:e*
+%:gs	cmdline.txt	/*%:gs*
+%:h	cmdline.txt	/*%:h*
+%:p	cmdline.txt	/*%:p*
+%:r	cmdline.txt	/*%:r*
+%:s	cmdline.txt	/*%:s*
+%:t	cmdline.txt	/*%:t*
+%:~	cmdline.txt	/*%:~*
 &	change.txt	/*&*
 '	motion.txt	/*'*
 ''	motion.txt	/*''*
@@ -1005,7 +1015,11 @@ $VIMRUNTIME	starting.txt	/*$VIMRUNTIME*
 'tw'	options.txt	/*'tw'*
 'tx'	options.txt	/*'tx'*
 'uc'	options.txt	/*'uc'*
+'udf'	options.txt	/*'udf'*
+'udir'	options.txt	/*'udir'*
 'ul'	options.txt	/*'ul'*
+'undodir'	options.txt	/*'undodir'*
+'undofile'	options.txt	/*'undofile'*
 'undolevels'	options.txt	/*'undolevels'*
 'updatecount'	options.txt	/*'updatecount'*
 'updatetime'	options.txt	/*'updatetime'*
@@ -1163,6 +1177,7 @@ $VIMRUNTIME	starting.txt	/*$VIMRUNTIME*
 +path_extra	various.txt	/*+path_extra*
 +perl	various.txt	/*+perl*
 +perl/dyn	various.txt	/*+perl\/dyn*
++persistent_undo	various.txt	/*+persistent_undo*
 +postscript	various.txt	/*+postscript*
 +printer	various.txt	/*+printer*
 +profile	various.txt	/*+profile*
@@ -2582,6 +2597,7 @@ $VIMRUNTIME	starting.txt	/*$VIMRUNTIME*
 :rubydo	if_ruby.txt	/*:rubydo*
 :rubyf	if_ruby.txt	/*:rubyf*
 :rubyfile	if_ruby.txt	/*:rubyfile*
+:rundo	undo.txt	/*:rundo*
 :runtime	repeat.txt	/*:runtime*
 :rv	starting.txt	/*:rv*
 :rviminfo	starting.txt	/*:rviminfo*
@@ -2964,6 +2980,7 @@ $VIMRUNTIME	starting.txt	/*$VIMRUNTIME*
 :write_f	editing.txt	/*:write_f*
 :ws	workshop.txt	/*:ws*
 :wsverb	workshop.txt	/*:wsverb*
+:wundo	undo.txt	/*:wundo*
 :wv	starting.txt	/*:wv*
 :wviminfo	starting.txt	/*:wviminfo*
 :x	editing.txt	/*:x*
@@ -6913,6 +6930,7 @@ perl-overview	if_perl.txt	/*perl-overview*
 perl-patterns	pattern.txt	/*perl-patterns*
 perl-using	if_perl.txt	/*perl-using*
 perl.vim	syntax.txt	/*perl.vim*
+persistent-undo	undo.txt	/*persistent-undo*
 pexpr-option	print.txt	/*pexpr-option*
 pfn-option	print.txt	/*pfn-option*
 pheader-option	print.txt	/*pheader-option*
@@ -7835,6 +7853,7 @@ undo	undo.txt	/*undo*
 undo-blocks	undo.txt	/*undo-blocks*
 undo-branches	undo.txt	/*undo-branches*
 undo-commands	undo.txt	/*undo-commands*
+undo-persistence	undo.txt	/*undo-persistence*
 undo-redo	undo.txt	/*undo-redo*
 undo-remarks	undo.txt	/*undo-remarks*
 undo-tree	undo.txt	/*undo-tree*
diff --git a/runtime/doc/todo.txt b/runtime/doc/todo.txt
index a109c2ea06..49fc70a4d5 100644
--- a/runtime/doc/todo.txt
+++ b/runtime/doc/todo.txt
@@ -30,6 +30,9 @@ be worked on, but only if you sponsor Vim development.  See |sponsor|.
 							*known-bugs*
 -------------------- Known bugs and current work -----------------------
 
+When Vim crashes it may run out of stack while executing autocommands.  Patch
+to not run autocommands when leaving Vim? (James Vega, 2010 May 23)
+
 Cursor positioning wrong with 0x200e character. (John Becket, 2010 May 6)
 
 E315 when trying to change a file in FileChangedRO autocommand event.
@@ -1082,6 +1085,18 @@ restored. (Luc St-Louis)
 
 Vim 7.3:
 Patches to include:
+8   Persistent undo bugs / fixes:
+    - Add tests.  Also with different 'enc'
+    - Add undofile(name): get undo file name for buffer "name".
+- Extend test62 for gettabvar() and settabvar(). (Yegappan Lakshmanan, 2010
+  May 23)
+- Also crypt the undo file.
+- Also crypt the swap file, each block separately.  Change mf_write() and
+    mf_read().  How to get b_p_key to these functions?
+- Do profiling on sha256 code to find obvious bottlenecks.
+- Do profiling on crypt code to find obvious bottlenecks.
+- Use off_t instead of long for bytes in a buffer. (James Vega, 2010 May 22,
+  update next day)
 - Include conceal patch?
   http://vince.negri.googlepages.com/
   http://vim.wikia.com/wiki/Patch_to_conceal_parts_of_lines
@@ -1150,42 +1165,17 @@ Needs some work:
   Needs some more testing.
   Update 2010 Apr 20, patch by Andy Kittner, May 16
 -   Easier/standard way to disable default plugins.
-8   Persistent undo: store undo in a file.  Patch by Jordan Lewis, 2009 Feb
-    20.  Repost 2009 Nov 16.
-    Get tar file from: http://repo.or.cz/w/vim_extended.git/tree/feat/persistent-undo
-    -> disable by default and add remark that it's new and may fail.
-    Testing remarks by Christian Brabandt, 2010 May 1:
-	- doesn't work well with symlinks (Jordan will look into it)
-	- old undo files tend to pile up
-        - :rundo should output a message (Jordan will fix this)
-    Bugs / fixes:
-    - Undo file should be stored with the original file by default, the undo
-      directory doesn't handle remote files or directory renames.
-      Use same mechanism as for swap files?  But only with one file name.
-    - Read coladd depending on FEAT_VIRTUALEDIT, should always read/write it
-    - invoke u_wundo() inside buf_write()
-    - invoke u_rundo() inside readfile()
-    - Document that ":wundo" and ":rundo" should only be used in autocommands.
-    - unserialize_pos() does not need a return value
-    - function comments go before the function, not inside
-    - u_get_undofile() changes its argument ffname
-    - make magic four bytes.
-    - errors need numbers "E000:"
-    - also put 'enc' in undo file.
-    - don't use timestamp, "touch file" or dir copy may change it and undo
-      still works.
-    Older ideas:
-    - Use timestamps, so that a version a certain time ago can be found and
-      info before some time/date can be flushed. 'undopersist' gives maximum
-      time to keep undo: "3h", "1d", "2w", "1y", etc.  For the file use dot
-      and extension: ".filename.un~" (like swapfile but "un~" instead of
-      "swp").
 -   ":{range}source": source the lines from the current file.
 	You can already yank lines and use :@" to execute them.
 	Most of do_source() would not be used, need a new function.
 	It's easy when not doing breakpoints or profiling.
+Probably not now:
+- Use timestamps for undo, so that a version a certain time ago can be found
+  and info before some time/date can be flushed. 'undopersist' gives maximum
+  time to keep undo: "3h", "1d", "2w", "1y", etc.
 Before (beta) release:
 - Add fixes for 7.2 to version7.txt
+- Rename vim73 branch to default (hints: Xavier de Gaye, 2010 May 23)
 
 
 More patches:
@@ -1292,7 +1282,6 @@ Awaiting updated patches:
     to left as well?  See patch of Dec 26. (Nadim Shaikli)
 8   Option to lock all used memory so that it doesn't get swapped to disk
     (uncrypted).  Patch by Jason Holt, 2003 May 23.  Uses mlock.
-7   Support a stronger encryption.  Jason Holt implemented AES (May 6 2003).
 7   Add ! register, for shell commands. (patch from Grenie)
 8   In the gzip plugin, also recognize *.gz.orig, *.gz.bak, etc.  Like it's
     done for filetype detection.  Patch from Walter Briscoe, 2003 Jul 1.
@@ -4320,11 +4309,6 @@ Mouse support:
 -   When mouse click after 'r' command, get character that was pointed to.
 
 
-Crypt and security:
-8   Also crypt the swapfile, each block separately.  Change mf_write() and
-    mf_read().  How to get b_p_key to these functions?
-
-
 Argument list:
 6   Add command to put all filenames from the tag files in the argument list.
     When given an argument, only use the files where that argument matches
diff --git a/runtime/doc/undo.txt b/runtime/doc/undo.txt
index 2c8c60c9aa..05e5555b77 100644
--- a/runtime/doc/undo.txt
+++ b/runtime/doc/undo.txt
@@ -12,7 +12,8 @@ The basics are explained in section |02.5| of the user manual.
 2. Two ways of undo		|undo-two-ways|
 3. Undo blocks			|undo-blocks|
 4. Undo branches		|undo-branches|
-5. Remarks about undo		|undo-remarks|
+5. Undo persistence		|undo-persistence|
+6. Remarks about undo		|undo-remarks|
 
 ==============================================================================
 1. Undo and redo commands				*undo-commands*
@@ -22,7 +23,7 @@ u			Undo [count] changes.  {Vi: only one level}
 
 							*:u* *:un* *:undo*
 :u[ndo]			Undo one change.  {Vi: only one level}
-
+								*E830*
 :u[ndo] {N}		Jump to after change number {N}.  See |undo-branches|
 			for the meaning of {N}.  {not in Vi}
 
@@ -109,6 +110,8 @@ change.
 To do the opposite, break a change into two undo blocks, in Insert mode use
 CTRL-G u.  This is useful if you want an insert command to be undoable in
 parts.  E.g., for each sentence.  |i_CTRL-G_u|
+Setting the value of 'undolevels' also breaks undo.  Even when the new value
+is equal to the old value.
 
 ==============================================================================
 4. Undo branches				*undo-branches* *undo-tree*
@@ -201,7 +204,88 @@ Note that using "u" and CTRL-R will not get you to all possible text states
 while repeating "g-" and "g+" does.
 
 ==============================================================================
-5. Remarks about undo					*undo-remarks*
+5. Undo persistence		*undo-persistence* *persistent-undo*
+
+When unloading a buffer Vim normally destroys the tree of undos created for
+that buffer.  By setting the 'undofile' option, Vim will automatically save
+your undo history when you write a file and restore undo history when you edit
+the file again.
+
+The 'undofile' option is checked after writing a file, before the BufWritePost
+autocommands.  If you want to control what files to write undo information
+for, you can use a BufWritePre autocommand: >
+	au BufWritePre /tmp/* setlocal noundofile
+
+Vim saves undo trees in a separate undo file, one for each edited file, using
+a simple scheme that maps filesystem paths directly to undo files. Vim will
+detect if an undo file is no longer synchronized with the file it was written
+for (with a hash of the file contents) and ignore it when the file was changed
+after the undo file was written, to prevent corruption.
+
+Undo files are normally saved in the same directory as the file.  This can be
+changed with the 'undodir' option.
+
+You can also save and restore undo histories by using ":wundo" and ":rundo"
+respectively:
+							*:wundo* *:rundo*
+:wundo[!] {file}
+		Write undo history to {file}.
+		When {file} exists and it does not look like an undo file
+		(the magic number at the start of the file is wrong), then
+		this fails, unless the ! was added.
+		If it exists and does look like an undo file it is
+		overwritten.
+		{not in Vi}
+
+:rundo {file}	Read undo history from {file}.
+		{not in Vi}
+
+You can use these in autocommands to explicitly specify the name of the
+history file.  E.g.: >
+
+	au BufReadPost * rundo %:h/UNDO/%:t
+	au BufWritePost * wundo %:h/UNDO/%:t
+
+You should keep 'undofile' off, otherwise you end up with two undo files for
+every write.
+Note: I did not verify this always works!
+
+Note that while reading/writing files and 'undofile' is set most errors will
+be silent, unless 'verbose' is set.  With :wundo and :rundo you will get more
+error messages, e.g., when the file cannot be read or written.
+
+NOTE: undo files are never deleted by Vim.  You need to delete them yourself.
+
+Reading an existing undo file may fail for several reasons:
+*E822*	It cannot be opened, because the file permissions don't allow it.
+*E823*	The magic number at the start of the file doesn't match.  This usually
+	means it is not an undo file.
+*E824*	The version number of the undo file indicates that it's written by a
+	newer version of Vim.  You need that newer version to open it.  Don't
+	write the buffer if you want to keep the undo info in the file.
+"Undo file contents changed"
+	The file text differs from when the undo file was written.  This means
+	the undo file cannot be used, it would corrupt the text.
+*E825* *E826*	The undo file does not contain valid contents and cannot be
+	used.
+*E827*	The magic number at the end of the file was not found.  This usually
+	means the file was truncated.
+
+Writing an undo file may fail for these reasons:
+*E828*	The file to be written cannot be created.  Perhaps you do not have
+	write permissions in the directory.
+"Will not overwrite with undo file, cannot read"
+	A file exists with the name of the undo file to be written, but it
+	cannot be read.  You may want to delete this file or rename it.
+"Will not overwrite, this is not an undo file"
+	A file exists with the name of the undo file to be written, but it
+	does not start with the right magic number.  You may want to delete
+	this file or rename it.
+*E829*	An error occurred while writing the undo file.  You may want to try
+	again.
+
+==============================================================================
+6. Remarks about undo					*undo-remarks*
 
 The number of changes that are remembered is set with the 'undolevels' option.
 If it is zero, the Vi-compatible way is always used.  If it is negative no
diff --git a/runtime/doc/various.txt b/runtime/doc/various.txt
index cfadfd629b..65688eead7 100644
--- a/runtime/doc/various.txt
+++ b/runtime/doc/various.txt
@@ -359,6 +359,7 @@ m  *+ole*		Win32 GUI only: |ole-interface|
 N  *+path_extra*	Up/downwards search in 'path' and 'tags'
 m  *+perl*		Perl interface |perl|
 m  *+perl/dyn*		Perl interface |perl-dynamic| |/dyn|
+H  *+persistent_undo*	Persistent undo |undo-persistence|
    *+postscript*	|:hardcopy| writes a PostScript file
 N  *+printer*		|:hardcopy| command
 H  *+profile*		|:profile| command
diff --git a/runtime/doc/version7.txt b/runtime/doc/version7.txt
index a6e1f61754..d59b622649 100644
--- a/runtime/doc/version7.txt
+++ b/runtime/doc/version7.txt
@@ -7170,6 +7170,10 @@ the buffer is marked as modified.
 Added							*added-7.3*
 -----
 
+Persistent undo: store undo information in a file.  Can undo to before when
+the file was read, also for unloaded buffers. |undo-persistence|
+(partly by Jordan Lewis)
+
 Added the 'relativenumber' option. (Markus Heidelberg)
 
 Support for Blowfish encryption.  Added the 'cryptmethod' option.
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index 06a76624d7..0ace4cc6d4 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -1032,6 +1032,10 @@ if has("vertsplit")
   call append("$", "cmdwinheight\theight of the command-line window")
   call <SID>OptionG("cwh", &cwh)
 endif
+call append("$", "undofile\tautomatically save and restore undo history")
+call <SID>BinOptionG("udf", &udf)
+call append("$", "undodir\tlist of directories for undo files")
+call <SID>OptionG("udir", &udir)
 
 
 call <SID>Header("executing external commands")
diff --git a/runtime/tutor/tutor.it b/runtime/tutor/tutor.it
index b1f6798d01..69e83eb03d 100644
--- a/runtime/tutor/tutor.it
+++ b/runtime/tutor/tutor.it
@@ -288,7 +288,7 @@ NOTA:  Se batti solo il movimento mentre sei in Modalità Normale, senza
 
   2. Batti  d2w  per cancellare le due parole MAIUSCOLE
 
-  3. Ripeti i passi 1 e 2 con un contatore diverso per cancellare la parole
+  3. Ripeti i passi 1 e 2 con un contatore diverso per cancellare le parole
      MAIUSCOLE consecutive con un solo comando
 
 --->  questa ABC DE linea FGHI JK LMN OP di parole è Q RS TUV ora ripulita.
diff --git a/runtime/tutor/tutor.it.utf-8 b/runtime/tutor/tutor.it.utf-8
index 051b51bbea..bee3f6d8f2 100644
--- a/runtime/tutor/tutor.it.utf-8
+++ b/runtime/tutor/tutor.it.utf-8
@@ -288,7 +288,7 @@ NOTA:  Se batti solo il movimento mentre sei in Modalità Normale, senza
 
   2. Batti  d2w  per cancellare le due parole MAIUSCOLE
 
-  3. Ripeti i passi 1 e 2 con un contatore diverso per cancellare la parole
+  3. Ripeti i passi 1 e 2 con un contatore diverso per cancellare le parole
      MAIUSCOLE consecutive con un solo comando
 
 --->  questa ABC DE linea FGHI JK LMN OP di parole è Q RS TUV ora ripulita.
diff --git a/src/buffer.c b/src/buffer.c
index 531e4b9a29..5ecb638727 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -61,8 +61,9 @@ static void buf_delete_signs __ARGS((buf_T *buf));
 #endif
 
 /*
- * Open current buffer, that is: open the memfile and read the file into memory
- * return FAIL for failure, OK otherwise
+ * Open current buffer, that is: open the memfile and read the file into
+ * memory.
+ * Return FAIL for failure, OK otherwise.
  */
     int
 open_buffer(read_stdin, eap)
diff --git a/src/eval.c b/src/eval.c
index 446df8ed3f..3c238fcbec 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -11869,6 +11869,9 @@ f_has(argvars, rettv)
 	"perl",
 #endif
 #endif
+#ifdef FEAT_PERSISTENT_UNDO
+	"persistent_undo",
+#endif
 #ifdef FEAT_PYTHON
 #ifndef DYNAMIC_PYTHON
 	"python",
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index 1ef885acdd..f41e0f449d 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -773,6 +773,8 @@ EX(CMD_rubydo,		"rubydo",	ex_rubydo,
 			RANGE|DFLALL|EXTRA|NEEDARG|CMDWIN),
 EX(CMD_rubyfile,	"rubyfile",	ex_rubyfile,
 			RANGE|FILE1|NEEDARG|CMDWIN),
+EX(CMD_rundo,		"rundo",	ex_rundo,
+			NEEDARG|EXTRA|XFILE),
 EX(CMD_rviminfo,	"rviminfo",	ex_viminfo,
 			BANG|FILE1|TRLBAR|CMDWIN),
 EX(CMD_substitute,	"substitute",	do_sub,
@@ -1061,6 +1063,8 @@ EX(CMD_wqall,		"wqall",	do_wqall,
 			BANG|FILE1|ARGOPT|DFLALL|TRLBAR),
 EX(CMD_wsverb,		"wsverb",	ex_wsverb,
 			EXTRA|NOTADR|NEEDARG),
+EX(CMD_wundo,		"wundo",	ex_wundo,
+			BANG|NEEDARG|EXTRA|XFILE),
 EX(CMD_wviminfo,	"wviminfo",	ex_viminfo,
 			BANG|FILE1|TRLBAR|CMDWIN),
 EX(CMD_xit,		"xit",		ex_exit,
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index ff39040cf7..4097f1d8f2 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -243,6 +243,10 @@ static void	ex_popup __ARGS((exarg_T *eap));
 # define ex_spellinfo		ex_ni
 # define ex_spellrepall		ex_ni
 #endif
+#ifndef FEAT_PERSISTENT_UNDO
+# define ex_rundo		ex_ni
+# define ex_wundo		ex_ni
+#endif
 #ifndef FEAT_MZSCHEME
 # define ex_mzscheme		ex_script_ni
 # define ex_mzfile		ex_ni
@@ -298,6 +302,10 @@ static void	ex_join __ARGS((exarg_T *eap));
 static void	ex_at __ARGS((exarg_T *eap));
 static void	ex_bang __ARGS((exarg_T *eap));
 static void	ex_undo __ARGS((exarg_T *eap));
+#ifdef FEAT_PERSISTENT_UNDO
+static void	ex_wundo __ARGS((exarg_T *eap));
+static void	ex_rundo __ARGS((exarg_T *eap));
+#endif
 static void	ex_redo __ARGS((exarg_T *eap));
 static void	ex_later __ARGS((exarg_T *eap));
 static void	ex_redir __ARGS((exarg_T *eap));
@@ -8452,6 +8460,28 @@ ex_undo(eap)
 	u_undo(1);
 }
 
+#ifdef FEAT_PERSISTENT_UNDO
+    void
+ex_wundo(eap)
+    exarg_T *eap;
+{
+    char_u hash[UNDO_HASH_SIZE];
+
+    u_compute_hash(hash);
+    u_write_undo(eap->arg, eap->forceit, curbuf, hash);
+}
+
+    void
+ex_rundo(eap)
+    exarg_T *eap;
+{
+    char_u hash[UNDO_HASH_SIZE];
+
+    u_compute_hash(hash);
+    u_read_undo(eap->arg, hash);
+}
+#endif
+
 /*
  * ":redo".
  */
diff --git a/src/feature.h b/src/feature.h
index 6b8f600ec0..61fe3345bb 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -1275,3 +1275,11 @@
 	    || defined(FEAT_BIG)
 # define FEAT_AUTOCHDIR
 #endif
+
+/*
+ * +persistent_undo	'undofile', 'undodir' options, :wundo and :rundo, and
+ * implementation.
+ */
+#ifdef FEAT_NORMAL
+# define FEAT_PERSISTENT_UNDO
+#endif
diff --git a/src/fileio.c b/src/fileio.c
index 7a697ee020..b7c86af7ef 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -253,6 +253,10 @@ readfile(fname, sfname, from, lines_to_skip, lines_to_read, eap, flags)
     char_u	*cryptkey = NULL;
     int		did_ask_for_key = FALSE;
 #endif
+#ifdef FEAT_PERSISTENT_UNDO
+    context_sha256_T sha_ctx;
+    int		read_undo_file = FALSE;
+#endif
     int		split = 0;		/* number of split lines */
 #define UNKNOWN	 0x0fffffff		/* file size is unknown */
     linenr_T	linecnt;
@@ -1178,6 +1182,12 @@ retry:
 #ifdef FEAT_MBYTE
 	conv_restlen = 0;
 #endif
+#ifdef FEAT_PERSISTENT_UNDO
+	read_undo_file = (newfile && curbuf->b_ffname != NULL && curbuf->b_p_udf
+				&& !filtering && !read_stdin && !read_buffer);
+	if (read_undo_file)
+	    sha256_start(&sha_ctx);
+#endif
     }
 
     while (!error && !got_int)
@@ -2133,6 +2143,10 @@ rewind_retry:
 			    error = TRUE;
 			    break;
 			}
+#ifdef FEAT_PERSISTENT_UNDO
+			if (read_undo_file)
+			    sha256_update(&sha_ctx, line_start, len);
+#endif
 			++lnum;
 			if (--read_count == 0)
 			{
@@ -2197,6 +2211,10 @@ rewind_retry:
 			    error = TRUE;
 			    break;
 			}
+#ifdef FEAT_PERSISTENT_UNDO
+			if (read_undo_file)
+			    sha256_update(&sha_ctx, line_start, len);
+#endif
 			++lnum;
 			if (--read_count == 0)
 			{
@@ -2237,11 +2255,17 @@ failed:
 	if (set_options)
 	    curbuf->b_p_eol = FALSE;
 	*ptr = NUL;
-	if (ml_append(lnum, line_start,
-			(colnr_T)(ptr - line_start + 1), newfile) == FAIL)
+	len = (colnr_T)(ptr - line_start + 1);
+	if (ml_append(lnum, line_start, len, newfile) == FAIL)
 	    error = TRUE;
 	else
+	{
+#ifdef FEAT_PERSISTENT_UNDO
+	    if (read_undo_file)
+		sha256_update(&sha_ctx, line_start, len);
+#endif
 	    read_no_eol_lnum = ++lnum;
+	}
     }
 
     if (set_options)
@@ -2555,6 +2579,19 @@ failed:
      */
     write_no_eol_lnum = read_no_eol_lnum;
 
+#ifdef FEAT_PERSISTENT_UNDO
+    /*
+     * When opening a new file locate undo info and read it.
+     */
+    if (read_undo_file)
+    {
+	char_u	hash[UNDO_HASH_SIZE];
+
+	sha256_finish(&sha_ctx, hash);
+	u_read_undo(NULL, hash);
+    }
+#endif
+
 #ifdef FEAT_AUTOCMD
     if (!read_stdin && !read_buffer)
     {
@@ -3038,6 +3075,10 @@ buf_write(buf, fname, sfname, start, end, eap, append, forceit,
     vim_acl_T	    acl = NULL;		/* ACL copied from original file to
 					   backup or new file */
 #endif
+#ifdef FEAT_PERSISTENT_UNDO
+    int		    write_undo_file = FALSE;
+    context_sha256_T sha_ctx;
+#endif
 
     if (fname == NULL || *fname == NUL)	/* safety check */
 	return FAIL;
@@ -4344,6 +4385,14 @@ restore_backup:
     write_info.bw_start_lnum = start;
 #endif
 
+#ifdef FEAT_PERSISTENT_UNDO
+    write_undo_file = (buf->b_p_udf && overwriting && !append
+					      && !filtering && reset_changed);
+    if (write_undo_file)
+	/* Prepare for computing the hash value of the text. */
+	sha256_start(&sha_ctx);
+#endif
+
     write_info.bw_len = bufsize;
 #ifdef HAS_BW_FLAGS
     write_info.bw_flags = wb_flags;
@@ -4358,6 +4407,10 @@ restore_backup:
 	 * Keep it fast!
 	 */
 	ptr = ml_get_buf(buf, lnum, FALSE) - 1;
+#ifdef FEAT_PERSISTENT_UNDO
+	if (write_undo_file)
+	    sha256_update(&sha_ctx, ptr + 1, STRLEN(ptr + 1) + 1);
+#endif
 	while ((c = *++ptr) != NUL)
 	{
 	    if (c == NL)
@@ -4886,6 +4939,20 @@ nofail:
     }
     msg_scroll = msg_save;
 
+#ifdef FEAT_PERSISTENT_UNDO
+    /*
+     * When writing the whole file and 'undofile' is set, also write the undo
+     * file.
+     */
+    if (retval == OK && write_undo_file)
+    {
+	char_u	    hash[UNDO_HASH_SIZE];
+
+	sha256_finish(&sha_ctx, hash);
+	u_write_undo(NULL, FALSE, buf, hash);
+    }
+#endif
+
 #ifdef FEAT_AUTOCMD
 #ifdef FEAT_EVAL
     if (!should_abort(retval))
diff --git a/src/memline.c b/src/memline.c
index b3c1727335..c3fdba3137 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -245,9 +245,6 @@ static char_u *make_percent_swname __ARGS((char_u *dir, char_u *name));
 #ifdef FEAT_BYTEOFF
 static void ml_updatechunk __ARGS((buf_T *buf, long line, long len, int updtype));
 #endif
-#ifdef HAVE_READLINK
-static int resolve_symlink __ARGS((char_u *fname, char_u *buf));
-#endif
 
 /*
  * Open a new memline for "buf".
@@ -3559,7 +3556,7 @@ ml_lineadd(buf, count)
     }
 }
 
-#ifdef HAVE_READLINK
+#if defined(HAVE_READLINK) || defined(PROTO)
 /*
  * Resolve a symlink in the last component of a file name.
  * Note that f_resolve() does it for every part of the path, we don't do that
@@ -3567,7 +3564,7 @@ ml_lineadd(buf, count)
  * If it worked returns OK and the resolved link in "buf[MAXPATHL]".
  * Otherwise returns FAIL.
  */
-    static int
+    int
 resolve_symlink(fname, buf)
     char_u	*fname;
     char_u	*buf;
@@ -3862,7 +3859,7 @@ do_swapexists(buf, fname)
  * Returns the name in allocated memory or NULL.
  *
  * Note: If BASENAMELEN is not correct, you will get error messages for
- *	 not being able to open the swapfile
+ *	 not being able to open the swap or undo file
  * Note: May trigger SwapExists autocmd, pointers may change!
  */
     static char_u *
@@ -3886,29 +3883,29 @@ findswapname(buf, dirp, old_fname)
 # define CREATE_DUMMY_FILE
     FILE	*dummyfd = NULL;
 
-/*
- * If we start editing a new file, e.g. "test.doc", which resides on an MSDOS
- * compatible filesystem, it is possible that the file "test.doc.swp" which we
- * create will be exactly the same file. To avoid this problem we temporarily
- * create "test.doc".
- * Don't do this when the check below for a 8.3 file name is used.
- */
+    /*
+     * If we start editing a new file, e.g. "test.doc", which resides on an
+     * MSDOS compatible filesystem, it is possible that the file
+     * "test.doc.swp" which we create will be exactly the same file. To avoid
+     * this problem we temporarily create "test.doc".  Don't do this when the
+     * check below for a 8.3 file name is used.
+     */
     if (!(buf->b_p_sn || buf->b_shortname) && buf->b_fname != NULL
 					     && mch_getperm(buf->b_fname) < 0)
 	dummyfd = mch_fopen((char *)buf->b_fname, "w");
 #endif
 
-/*
- * Isolate a directory name from *dirp and put it in dir_name.
- * First allocate some memory to put the directory name in.
- */
+    /*
+     * Isolate a directory name from *dirp and put it in dir_name.
+     * First allocate some memory to put the directory name in.
+     */
     dir_name = alloc((unsigned)STRLEN(*dirp) + 1);
     if (dir_name != NULL)
 	(void)copy_option_part(dirp, dir_name, 31000, ",");
 
-/*
- * we try different names until we find one that does not exist yet
- */
+    /*
+     * we try different names until we find one that does not exist yet
+     */
     if (dir_name == NULL)	    /* out of memo